Recently, as one technique for improving a recording density of a magnetic disk device, a thermally assisted magnetic recording has been proposed. This thermally assisted magnetic recording is a technique for applying a magnetic field and heat to a small region of a recording medium to record data. As a method for heating a small region of a recording medium, a near-field optical element is considered. This near-field optical element is provided near a magnetic recording element of a head slider, and converts light introduced from an external light emitting element into near-field light for output, thereby heating a small region of a recording medium. In JP-A-2007-335027, there is disclosed a thermally assisted magnetic recording head on which a sub-mount for mounting a light emitting element between a head supporting member and a head slider is provided.